The present invention relates generally to the field of communications technology.
Fiber optics is the science of transmitting data, voice, and images by the passage of light through thin, transparent fibers. In telecommunications, fibre optic technology has virtually replaced copper wire in long-distance telephone lines, and it is used to link computers within local area networks.
The basic medium of fiber optics is a hair-thin fiber that is sometimes made of plastic but most often of glass. A typical glass optical fiber has a diameter of 125 micrometers, or 0.125 mm (0.005 inch). This is actually the diameter of the cladding, or outer reflecting layer; the core, or inner transmitting cylinder, may have a diameter as small as 10 m. Through a process known as total internal reflection, light rays beamed into the fiber can propagate within the core for great distances with remarkably little attenuation, or reduction in intensity. The degree of attenuation over distance varies according to the wavelength of the light and to the composition of the fiber. When glass fibers of core/cladding design were introduced in the early 1950s, the presence of impurities restricted their employment to the short lengths sufficient for endoscopy. In 1966, electrical engineers K. C. Kao and G. A. Hockham, working in England, suggested using fibers for telecommunication, and within two decades silica glass fibers were being produced with sufficient purity that infrared light signals could travel through them for 100 km (60 miles) or more without having to be boosted by repeaters. Plastic fibers, usually made of polymethyl methacrylate, polystyrene, or polycarbonate, are cheaper to produce and more flexible than glass fibers, but their greater attenuation of light restricts their use to much shorter links within buildings or automobiles.
Optical telecommunication is usually conducted with infrared light. Infrared light is efficiently generated by light-emitting diodes or semiconductor lasers and suffers the least attenuation in glass fibers.
In 1898, the US Post Office Department began a large scale project, employing pneumatic tube systems to deliver mail in large urban areas. These tube systems used pressurized air to move a two foot by eight inch mail canister through an underground eight-inch cast iron pipe. This pneumatic system, known as The Twentieth Century Limited, was constructed to send priority and first-class mail between a city""s central post office and connecting neighborhood post offices, avoiding road congestion and inclement weather. The pneumatic system was built in five cities (NYC, Boston, Philadelphia, Chicago and St. Louis); and construction was authorized in five others (Baltimore, Cincinnati, Kansas City, Pittsburgh and San Francisco). At its greatest expansion, there were over one-hundred and thirteen miles of mail tubes delivering as many as two-hundred thousand letters per tube every hour.
When the system was first installed, pneumatic transport was one of the greatest technological wonders available, and was commonly regarded, when combined with an effective railroad infrastructure, to be the greatest possible method for the delivery of mail and goods. Former Postmaster Robert Emory Smith, in 1900, predicted that one day every household would be linked to every other by means of pneumatic tubes. There were even several proposals around the turn of this century to build a tube system between North America and Europe. The tubes could carry a greater volume of messages than could be dispatched by the telegraph and were much faster than a horse-drawn wagonxe2x80x94at that time, the most common vehicle for mail delivery.
The pneumatic tube service continued in most cities until 1918. In New York City, the tube system remained in operation until Dec. 1, 1953, when it was suspended pending an internal review. The pneumatic system was discontinued permanently later that December when the Post Office terminated the contract for service. New York Mail and Newspaper Transportation Company, the owner of the pipes, was then ordered to remove the equipment from Post Office buildings. The tubes were abandoned to the City of New York in 1954 and were not subsequently used. In certain cities in Europe, the tubes were converted to accommodate telephone and telegraph wires.
Within Manhattan, the tube system ran for twenty-six miles, from the old Customs House by Battery Park to Harlem and back routing through Times Square, Grand Central Station and the main Post Office by Penn Station. Two eight-inch pipes were used along each route, one for sending the other for receiving. The pipes are completely airtight and are buried four to six feet underground; though in some places, the tubes are located within subway tunnels. The mail canisters were two feet long and just under eight inches in diameter in order to fit within the iron pipes. Each canister had a felt/leather packing on each end, to make an airtight seal, as well as four small wheels which helped prevent the canister from getting lodged at a junction in the pipes. The tubes are 8 and xe2x85x9 inch internal diameter cast iron pipe, with a {fraction (9/16)} inch wall.
In accordance with a first embodiment of the present invention, a method for inserting fiber optic cables in a pneumatic tube system is provided which comprises the steps of accessing a pneumatic tube network at at least two termination points and feeding a fiber optic cable through the pneumatic tube via the at least two termination points. In accordance with further aspects of this embodiment, the step of feeding further comprises inserting a movable camera device at a first one of the at least two termination points, moving a guide cable from the first one of the at least two termination points through the pneumatic tube network to the second one of the at least two termination points; and pulling a fiber optic cable along the guide cable from the first one of the at least two termination points through the pneumatic tube network to the second one of the at least two termination points. In accordance with still further aspects of this embodiment, the step of moving a guide cable further includes inserting a movable camera device at one of the termination points and connecting a guide cable thereto; and moving the camera with the guide cable from the first one of the at least two termination points through the pneumatic tube network to the second one of the at least two termination points. In this regard, the movable camera may be used to assess damage to the pneumatic tubes based upon images generated by the movable camera.
After installation of the fiber optic cables, maintenance on the fiber optic cables and the pneumatic tube network can be performed at any time by accessing the pneumatic tubes at at least two points, inserting a movable camera device at one of the points and connecting a guide cable thereto; moving the camera with the guide cable from the first one of the at least two points through the pneumatic tube network to the second one of the at least two points, and assessing damage to the pneumatic tubes and fiber optic cables based upon images generated by the movable camera.
In accordance with a second embodiment of the present invention, a method for inserting communications cables in a pre-existing tube system. In this regard, a pre-existing tube system is defined as a network of tubes which were previously installed underground for a purpose other than transmitting communications signals. In accordance with this embodiment, the method comprising the steps of: accessing a pre-existing tube network at at least two termination points, inserting a movable camera device at a first one of the at least two termination points, moving a guide cable from the first one of the at least two termination points through the tube network to the second one of the at least two termination points, and pulling a communications cable along the guide cable from the first one of the at least two termination points through the tube network to the second one of the at least two termination points. The communications cable can, for example, be a fiber optic cable, a copper cable, a co-axial cable, or any other cable conventionally used to communicate voice, data, and/or video signals. Similar to the first embodiment, the step of moving a guide cable may further include inserting a movable camera device at one of the termination points and connecting a guide cable thereto; and moving the camera with the guide cable from the first one of the at least two termination points through the pneumatic tube network to the second one of the at least two termination points in a In accordance with certain aspects of this embodiment, the pre-existing tube network is comprised of tubes having an interior diameter of between 8 and 9 inches. A non-limiting example of such a tube network is the pneumatic tube network described above in the background of the invention section.
In accordance with a third embodiment of the present invention, a communication system is provided which includes a pneumatic tube network; a plurality of terminals coupled to the pneumatic tube network via conduits; and one or more fiber optic cables disposed within the pneumatic tubes, at least one fiber optic cable connecting at least two of the plurality of terminals.